1. Field of the Invention
The present invention, relates to a method for the surface treatment of vacuum materials, and more particularly, it relates to a method for the surface treatment of vacuum materials which are used, for example, in vacuum apparatus for thin film deposition purposes in which semiconductors and electronic parts are produced.
2. Description of Related Art
In the past, it has been necessary with vacuum materials such as stainless steel which are used in vacuum apparatuses for thin film processing purposes, for example, to reduce the amount of gas which is released from the surface of the materials and to reduce the gas sticking probability of the surface. Water (H2O) which is always present and which has a strong oxidizing action is especially important as such a gas. A surface treatment which can reduce the xe2x80x9camount of H2O releasedxe2x80x9d and reduce the xe2x80x9cH2O sticking probabilityxe2x80x9d is very desirable. The xe2x80x9camount of H2O releasedxe2x80x9d signifies the amount of water which is released from the surface into the space when a vacuum material which has been present in an environment at atmospheric pressure is pumped out to a vacuum environment. On the other hand, the xe2x80x9cH2O sticking probabilityxe2x80x9d signifies the proportion of the H2O which does not rebound, but rather sticks to the surface of the vacuum material when H2O is colliding with the surface of the vacuum material in the vacuum environment.
The units of the xe2x80x9cH2O sticking probabilityxe2x80x9d reflect the number of H2O molecules that will stick. For example, an xe2x80x9cH2O sticking probabilityxe2x80x9d of 2xc3x9710xe2x88x923 means that two H2O molecules out of each one thousand molecules will stick.
Much research has been carried out into methods of surface treatment for reducing the xe2x80x9camount of H2O releasedxe2x80x9d, and some of these methods have been put into practical use. These are generally methods in which the surface of the vacuum material is polished wherein an undesirable modified surface layer is removed either mechanically or chemically. Conversely, coating methods in which a film which has desirable properties is formed over the whole surface of the vacuum material are also in general use. Examples of such films include Cr2O3 films (chromium oxide films) obtained by oxidizing the surface of the material itself, Si films (silicon films and silicon oxide films), and TiN films (titanium nitride films) which are obtained by deposition from the outside, and BN films (boron nitride films) which are obtained by diffusion from within the material. Cr2O3 films have been disclosed in Japanese Unexamined Patent Applications (Kokai) H6-41629 and H6-116632, silicon oxide films have been disclosed in Japanese Unexamined Patent Application (Kokai) H4-337074 and BN films have been disclosed in Japanese Unexamined Patent Applications (Kokai) H7-62431 and H4-263011.
Conventional surface treatments, as described above, are all carried out to reduce the xe2x80x9camount of H2O releasedxe2x80x9d, and their effect has been evaluated just on the basis of the extent of the xe2x80x9camount of H2O releasedxe2x80x9d. The other factor, namely the xe2x80x9cH2O sticking probabilityxe2x80x9d, has not been evaluated at all. This is mainly because it is very difficult to measure precisely the xe2x80x9cH2O sticking probabilityxe2x80x9d, but it is also because it was thought generally that the two values were proportional, which is to say that the xe2x80x9cH2O sticking probabilityxe2x80x9d should also fall as a result of a surface treatment which reduces the xe2x80x9camount of H2O releasedxe2x80x9d.
An example of an investigation of surface treatment methods which measure the value of the xe2x80x9cH2O sticking probabilityxe2x80x9d precisely is found in Japanese Unexamined Patent Application (Kokai) H9-91606. According to that application, the xe2x80x9cH2O sticking probabilityxe2x80x9d is reduced by heating stainless steel in a specified atmosphere. However, care must be taken with handling the material after the treatment and, moreover, the values achieved are not satisfactory.
An object of the present invention is to provide a practical method for the surface treatment of vacuum materials with which the xe2x80x9cH2O sticking probabilityxe2x80x9d is reduced satisfactorily.
The importance of the xe2x80x9cH2O sticking probabilityxe2x80x9d on the vacuum materials used in vacuum apparatus for thin film processing, for example, will be described first of all.
The main component of the residual gas in a vacuum apparatus before baking (heating while pumping out and de-gassing) is H2O, and the pressure in the vacuum apparatus before baking is determined principally by the xe2x80x9camount of H2O releasedxe2x80x9d. However, when baking the vacuum apparatus, the H2O pressure falls by a few orders of magnitude. Hence, for a vacuum apparatus which has once been subjected to baking, the xe2x80x9camount of H2O releasedxe2x80x9d becomes virtually insignificant. The latest vacuum apparatus for thin film processing purposes for the production of semiconductors and electronic parts is usually provided with a load-lock mechanism, and once baking has been carried out and the pressure has been reduced, the apparatus is operated continuously for a few weeks or even a few months while being maintained in a vacuum state. Thus, the effect of the xe2x80x9camount of H2O releasedxe2x80x9d is only seen when the vacuum state has been broken for maintenance purposes and the system is put back into service after it has been exposed to atmospheric pressure.
On the other hand, even when baking has been carried out and the H2O pressure has been reduced, a large amount of H2O is released from the surface as a result of irradiation with energy beams or plasma, for example, and if the H2O pressure increases at such a time, then it is known that a very long period of time is required to return to the original pressure. The amount of H2O which is released at this time and the time taken to recover are determined mainly by the magnitude of the xe2x80x9cH2O sticking probabilityxe2x80x9d. Thus, if the xe2x80x9cH2O sticking probabilityxe2x80x9d is high, then a large amount of H2O sticks to the wall, and the time taken for the H2O which has been released into the space to reach the exhaust port is also considerable. In such a case, the pumping efficiency is also poor. Now, energy beams and plasma are certainly generated in the film deposition operating state when cleanliness is essential in thin film processing. Hence, it is not the xe2x80x9camount of H2O releasedxe2x80x9d but the xe2x80x9cH2O sticking probabilityxe2x80x9d which is the greatest problem in the thin film processing of semiconductor and electronic part production.
Accordingly, the method for the surface treatment of vacuum materials of this invention is intended to lower the H2O sticking probability on the surface of the vacuum material.